1. Field of the Invention
This invention relates generally to sound emitting apparatus, and particularly to a diaphragm for loudspeakers.
2. Prior Art
Recently, it has been required that loudspeakers have acoustic characteristics superior to conventional loudspeakers in industrial fields in connection with cassette tape recorders, micro cassette recorders, and hi-fi stereos. With this requirement, the performance of diaphragms of the loudspeakers has also been considered as an important factor.
As is well known in the prior art, loudspeakers usually comprise a vibration system such as a diaphragm, a voice coil bobbin, and a voice-coil, and further comprise a magnetic circuit system such as a magnet, a pole piece, a top plate and a yoke. When an audio-frequency signal is applied to a lead of the voice-coil which is placed in a uniform magnetic field, the voice-coil will move either inward or outward by generating electromagnetic forces, depending on the instantaneous polarity of the applied audio signal. Thus, loudspeakers are electroacoustic transducers used for the purpose of transforming electrical energy into acoustical energy through the mechanical motion of the diaphragm, so that acoustic waves are emanated from the diaphragm.
As an ideal diaphragm for the loudspeakers, it is required that the diaphragm moves like a piston in response to any frequency within a frequency band which is to be used. If deformation of the diaphragm or partial vibration comes out during the vibrations thereof, high-fidelity reproducing cannot be actualized due to deterioration of a sound pressure-frequency response of a distortion factor, and of a phase response, etc.
However, according to conventional paper cone diaphragms and plastic diaphragms, since E/.rho. (wherein E is a Young's modulus, and .rho. is a density) of these diaphragm materials is small, a high resonant frequency thereof is low. Therefore, there is a drawback that conventional loudspeakers cannot perform reproduction with high fidelity in response to the frequency in a high frequency band.